Answer Posted / vipul dhruv

basically vfd is a soft starter which is used for induction
machines. there are two methods of control on which a vfd
works... one is the vector control & the other is the scalar
control method. your question does not concern this so no
explanation is required i guess... now the function of the
vfd is to maintain a constant flux in the air gap of the
machine it is used for and that can be achieved only when
the V/HZ ratio of the machine is kept constant.so a ramp is
created in a vfd by the controller which gives a constant
v/hz ratio... and the flux is kept constant... by flux i
mean the magnetic flux.. so as the frequency varies the
voltage has to vary accordingly to keep the ratio constant
which is fed into the controller....the controller is the
heart of the vfd...

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